Howdy, I have an Erika model M with aftermarket keyswaps and some discoloration.  As far as I can tell, a few of the key caps are hand drawn on the flip side of the cardboard discs.  I'm debating if I should redo them entirely or just clean out the crud.  Also, the left shift cap came off in shipping and appears to be yellowed celluloid instead of glass. Where do folks get glass replacements?  I'm assuming ebay or a donor machine. 

Any tips or tricks from the community?  I found this blog post and am still researching.  Is there a better method?